The present invention relates to a catheter for artificial insemination. More specifically, the present invention relates to a catheter for artificial insemination which is used for sucking in semen, which is collected from humans, washed and concentrated (sperm suspension), and injecting the same into a uterine cavity.
An Assisted Reproductive Technology (ART) such as artificial insemination or in vitro fertilization is a method for bypassing a part or whole of a process in which a sperm travels up a female reproductive route, fertilizes an egg cell and is fused with an egg cell. According to ART, even in a case in which the number of sperm is extremely small in ejaculated semen or a case in which sperm in semen are lacking in an ability to enter into an egg cell by their own power (fertilizability), fertilization is theoretically possible so long as one sperm and one egg cell exist. The sperm used here may be ejaculated sperm, epididymis sperm or testicle sperm.
In ART, it is important to use morphologically normal motile sperm withdrawn from semen in fertilization. Accordingly, the semen is washed and concentrated to selectively collect motile sperm which are used in fertilization.
A method for selectively collecting motile sperm is roughly classified into a method using centrifugation and a method using motility of sperm per se. The method using centrifugation is a method in which semen is laminated on a density gradient material such as sucrose polymer ficoll, modified colloidal silica gel or percoll, the lamination consisting of semen and the density gradient material is centrifuged to provide a continuous density gradient and a layer of a sperm suspension containing motile sperm in the centrifuged lamination is selectively collected. Motile sperm lose cytoplasm during formation and maturation thereof, and they are high in density compared to bacteria having cytoplasm or immotile sperm. In the method using centrifugation, since only motile sperm are concentrated in a deposit, the deposit is collected to enable the selective collection of motile sperm.
Meanwhile, the method using motility of sperm per se includes a swim-up method, a swim-down method and so on. The swim-up method is a method in which the sperm suspension obtained by the method using centrifugation or the like is allowed to stand in a culture solution and sperm swimming up in the culture solution by their own motility are recovered. The swim-down method is a modified method of the swim-up method used in a case that semen is found defective.
In order to inject the sperm suspension obtained by the foregoing method into a uterine cavity, a fertilization needle made of metal has so far been used. This fertilization needle is used for sucking in a sperm suspension from a distal end side of the needle with a syringe connected with a proximal end side of the needle. The sperm suspension sucked in the syringe is injected from the distal end side of the needle while the distal end side is inserted into a uterine cavity from a vagina via a uterine cervix. Further, a fertilization needle (catheter) made of a flexible material is also used instead of the fertilization needle made of metal.
In many of these conventional fertilization needles, a distal end of the needle is closed and a side hole is formed in a section of a distal end side of the needle. Such a needle does not have a likelihood that, when the distal end of the needle is open, foreign matter in a vagina, vaginal secretions and the like might intrude in the needle from the open end to clog an injection route for a sperm suspension. However, the fertilization needle having such a structure cannot suck or draw in, when sucking a sperm suspension stored in a container such as a test tube, a total amount of the sperm suspension in the container. Even though the suspension is sucked in by inclining the container, the procedure is troublesome and a slight amount of the suspension remains in the container.
Further, since the fertilization needle is used to suck a sperm suspension into a syringe connected with a proximal end portion of the needle, the role of the needle itself is only to pass the suspension. Accordingly, the fertilization needle is formed with a small outer diameter and has a small inner volume because the highest priority is easy insertion into a uterine cavity. Nevertheless, a total amount of a sperm suspension sucked into the syringe is actually not discharged into a uterine cavity and a slight amount of the suspension remains in a connected portion between the syringe and the needle. The suspension remaining in the connected portion while sucking in and injecting can cause a serious problem of reducing the probability of pregnancy particularly in a case that only a small amount of semen is collected.
Moreover, in a fertilization needle having such a small outer diameter, a space is formed between the needle and a wall of a uterine cervix in insertion of the needle into a uterine cavity. As a result, there is a likelihood that a sperm suspension flows out of a uterine os during a procedure of injecting the sperm suspension. Accordingly, a method has been studied in which a flange is mounted on a proximal end portion of the fertilization needle and closely attached to a uterine os while injecting the suspension to prevent outflow of the suspension (Japanese Patent No. 2681345, et al.). However, in the fertilization needle having such a structure, the number of parts is increased, which makes it more difficult to manufacture the fertilization needle and increases the cost of the fertilization needle.